Question on Life Drain

Ok I need a spell that constantly causes damage to the unit while it is in range and if it walks out of range your unit follows it until stated otherwise. I figured life drain would work fine for this, but I don't know how to make it follow the unit, and I don't know how to make it not give life back to you. So if you can help me with life drain, or know some other way to accomplish this, please help.

I don't think there is a way, because anything you do to cause the unit to follow the targeted unit will stop the Life Drain ability. Removing the Channel Tag from the Ability might work, but I'm not sure exactly how Life Drain Works, but what you want to do will probably require a trigger.

you could base the spell off heal, and make it all negative?? that way your unit doesnt stop attack until the target is dead or you have no mana, you can also auto cast it...

it take a bit of fiddling around, like making the dmg and the targets right

Heal can't be used on units with full health.

The best way would be to trigger the whole thing, because there are so many elements that the war3 engine does not support (maintaining the spell while moving, for example). The complexity of the solution depends greatly on the trigger spell system you are using (if you already have one anyway), and on the multi instancability you want to have (can there be more heroes of the same type at once in the game? can a single player have more than one hero?...). Let me know these things so I (or anyone else) can help you figure out the best triggers to do this.

How about giving it shadow strike and you change the buff to any icon and using trigger to follow the target.
There's a way to counter this effect though, have to figure out how to cancel the strike if caster decides not to follow. :\

That's not a problem, you can remove buffs from units with triggers. The spell will, of course, require variables to keep track of the affected unit. How to use variables depends on the system you use.